South: Rain, frosts and difficult disease control

It’s fair to say weather has been our issue this month, and there’s been plenty of it. 

So far, up to the point of writing (29th April), we have had 23 days where it has rained amounting to a total of 95mm. In addition we’ve had six air frosts, about 10 ground frosts and an average temperature of 8.6deg C. Over the month soil temperatures have dropped from 12deg to 5deg and are now back up to 8 or 9deg..

Unsurprisingly not many T1s have been applied so far. Every opportunity to spray must now be used as disease levels are rising rapidly. Septoria is just visible on the top leaves of crops in a lot of places but with the cold weather rusts and mildew levels are very low. Leaf three has emerged on nearly all wheat crops, while later ones have leaf two part-emerged. It is important to target the T1s to the most forward crops first.

Thinking a few weeks ahead, it is important to remember that the flag leaf contributes 45-50% of the yield so even if T1s have only just gone on, once the flag is out it’s time to go again and with disease levels high don’t cut back the rates. Even if the T1 is applied very late I would not risk cutting the rates of either as disease pressure is rising rapidly and you don’t need to protect much yield to pay for the extra cost of fungicide.

Winter rape is flowering well.  On many crops the main raceme is about 75% complete.  Even though the weather hasn’t been good for bees or other pollinators, the pod set is looking good. In areas where there aren’t many pods on the main raceme, there is plenty of time for crops to compensate so hopefully yield will not be affected. Lower population crops are branching very strongly and have filled the ground that they have been given.  

Sclerotinia is now the key focus. Germination is continuing, petals are falling and temperatures are slowly rising. The threat is now high so sclerotinia sprays need applying if they haven’t been done yet. Don’t leave the gap between the first and second spray wider than three weeks as products are protectant not curative. Galileo (picoxystobin), Filan (boscalid) or Amistar (azoxystrobin) are the most sensible options, but don’t forget to add a partner for powdery mildew and light leaf spot.

At the moment I’m recommending 0.25kg Filan plus 0.75kg Monkey (Tebuconazole and Prochloraz) for my second sclerotinia spray, but if this wet weather continues, using Compass (Iprodione + Thiophanate-methyl) will become the better choice for its alternaria control – something we haven’t really had to worry about for about ten years.  Coverage of the petals is crucial, so it’s one of the areas where high water rates are needed. 

My biggest worry at the moment is the state of the early-drilled grain maize crops. They have had to endure all this wet weather and will be sitting in very damp seedbeds, some of which are flooded.  I haven’t dared look for 10 days, but some seed may well be rotting by now.  Those that are waiting get drilling may have to wait some time for seedbeds to dry out.  Don’t be tempted to maul them in, patience is the key.  May drilled crops can still yield well, as they often emerge within a week and then never stop growing (assuming that we get some warm, dry weather).

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